Ultraviolet light treatment of waste milk evaluated

Common pathogens in colostrum and milk, such as Escherichia coli, Listeria monocytogenes, Mycoplasma species, Salmonella species, Streptococcus species, Staphylococcus species, Campylobacter species, and Mycobacterium avium subspecies paratuberculosis (MAP, a.k.a. Johne’s Disease) can be transmitted when fed to calves. In order to reduce the bacterial load, many dairies successfully pasteurize colostrum and waste milk. There are some dairies that are using ultraviolet (UV) light treatment as an alternative to pasteurization. However, until recently there has been little evidence to support the use of UV light with milk.

Ultraviolet light treatment is used routinely for drinking water globally and in the food-processing industry for items such as juice. The UV light inactivates bacteria by affecting DNA and preventing bacteria from reproducing. However, the effectiveness of the UV light at inactivating bacteria is influenced by the type and number of bacteria present, the amount of UV light used, and the solids content of the liquid. Interestingly, UV light is starting to be used to treat donor human milk to reduce the vegetative bacteria by 100,000 fold to meet requirements of milk bank guidelines. Higher doses of UV light are needed when the total solids content of the human milk is increased. The solids content issue might be a concern when treating colostrum vs. waste milk on-farm.

Cornell researchers used a UV light treatment system similar to the commercially available UV Pure system (GEA Farm Technologies) and treated whole milk and colostrum that were inoculated with several types of bacteria (i.e. Listeria innocua, Mycobacterim smegmatis, Salmonella, E. coli, Staphylococcus aureus, Steptococcus agalactiae, and Acinetobacter baumannii). They found that UV light treatment significantly reduced (~1,000 fold) all bacterial species tested except for M. smegmatis (a surrogate for the pathogenic MAP) in whole milk. In contrast, UV light treatment of colostrum only reduced Listeria, Salmonella and A. baumannii by ~10 fold even though the colostrum was exposed to more cycles of UV radiation. The UV light is limited in its ability to penetrate the liquid because of high solids content of colostrum (~6.7% fat, 14% protein) relative to milk (4% fat, 3.1% protein). The UV light treatment lowered the concentration of IgG in colostrum up to 50% in proportion with length of time treated. In another study, IgG was shown to be reduced up to 42% with UV treatment compared with untreated colostrum.

Penn State researchers evaluated the UV Pure system for waste milk on nine Pennsylvania dairies and found that UV light treatment was effective for some but not all bacteria types found in waste milk. In general bacteria were reduced ~10 to 100 fold. Coliforms, Streptococcus agalactiae, Staphylocuccus aureus, environmental streptococci, and contagious streptococci were reduced by more than 50%. Research from the United Kingdom has shown that MAP is more resistant to UV light (i.e. less than a10-fold reduction) than other bacteria found in milk, suggesting that UV light is not a viable alternative to pasteurization for reductions in MAP.

A recent study used the UV Pure system to treat waste milk on a dairy and found significant reductions (10 to 1,000 fold) in bacterial counts for E. coli, Staph. aureus, and Streptococcus species. In the same study, waste milk was pasteurized at 162°F for 15 seconds and reduced the bacterial counts 10 to 100,000 fold. The researchers concluded that overall heat treatment of waste milk was more effective than UV treatment of waste milk in decreasing bacterial counts. Also, colostrum that was pasteurized at 145°F for 60 minutes had greater reductions in bacterial counts than colostrum that was treated with UV light. Interestingly, colostrum that was either heat treated or UV treated had lower IgG concentration than untreated colostrum. However, there were no differences in serum IgG concentrations among calves fed the colostrum treated differently.